Lloyds Banking Group joins Deutsche Bank, Citigroup, JPMorgan Chase, Royal Bank of Scotland, Barclays, HSBC and UBS to increase the number of banks under examination by the two state prosecutors to 16.

The other eight also under investigation as of Friday are Bank of America, Bank of Tokyo Mitsubishi UFJ, Credit Suisse, Rabobank, Royal Bank of Canada, Société Générale, Norinchukin Bank and West LB.

Barclays has already been hit with a £290 million fine after the Financial Services Authority declared staff at the bank had repeatedly made false submissions to help set Libor.

Alongside the UK and the US, Japanese and Canadian authorities are also investigating Libor rigging. Libor is hugely important because it is used to price trillions of pounds’ worth of financial instruments including home mortgages and derivatives.

A spokesman for Lloyds Banking Group told Huff Post UK: "As with many others in the sector, the group is assisting various regulators in their ongoing investigations into the setting of the London Interbank Offer Rate. Until these investigations are completed, it would be inappropriate for us to comment any further.”